Understanding The Triumph ECU Starting Issue

With some Triumph motorcycles, including the early modern classic bikes (Bonneville, Thruxton, Scarmbler), there is a known issue with the computer preventing the starter from working. The ECU or ECM monitors battery voltage when you turn the key and if that voltage is below a certain threshold, the ECU will not allow the starting circuit to engage the starter, even though the battery might be capable of turning over the starter! The result is a "click" of the starter relay and nothing else. So, if your bike has been sitting awhile or the battery is just slightly undercharged, it may not start.

The solution could be a good charge on the existing battery or it could mean you need a new battery. In this video I'll show some testing you can do and I'll try to narrow down the voltage range that should give you concern.


UPDATE: A sharp eyed viewer noticed that I traced the wrong path on the wiring diagram with my finger when I was discussing the control of the ground by the ECU. The conclusion is the same, but look at the diagram not my finger!